1. Field of the Invention
This invention relates to flame retardant polyester resin compositions reinforced with glass fiber having outstanding mechanical and thermal properties as well as good moldability.
2. Description of the Prior Art
Glass fiber reinforced products produced with polyethylene terephthalate resin have been used in numerous applications as a type of engineering plastic. Such reinforced resins are known for their outstanding mechanical and thermal properties, and chemical resistance as well as good moldability.
However, the glass fiber reinforced polyester resin has the distinct disadvantage of flammability, as do other synthetic resins. Accordingly flame retardancy is an important property for engineering plastics.
Normally untreated polyethylene terephthalate resin products reinforced with glass fiber require a comparatively high molding temperature, for example in the range of about 250.degree. to 300.degree. C. This means that the heat resistance of a flame retardant is important. This means one must use flame retardants that will be hardly decomposed at the high temperature. Further, they must not impart color to nor deteriorate the resin properties in the ultimately molded products. Since glass fiber reinforced polyethylene terephthalate resin products have a high heat distortion temperature, they are typically used in comprehensive applications exposed to high temperature, for example in electric appliances and the like. Accordingly, the successful flame retardation of polyester resin/glass fiber reinforced products, as mentioned above, requires the molded articles to be thermally stable. That is, they should be free from deterioration in their flame retardant properties due to heat dissipation if the finished products are exposed to high temperature over long term operations while still providing the required basic properties which include flame retardance, mechanical strength, heat resistance and the like.
We previously found that the flame retardant represented by the general formula (II), described below, is excellent in the heat resistance and flame retardancy and we tried to improve the flame retardancy of glass fiber reinforced polyethylene terephthalate resin products by incorporating this flame retardant together with antimony trioxide into glass fiber reinforced polyethylene terephthalate resin composition. However, further investigations have revealed that if it is intended to obtain a high flame retardance by incorporating a large amount of the flame retardant represented by the general formula (II) into glass fiber reinforced polyethylene terephthalate resin products, the mechanical strength is reduced and also the moldability (the cut-off property at the time of extrusion) is degraded.